1. Field of the Invention
This invention relates to an edge-of-dock type dock leveler which is operable as a runoff guard for a loading dock platform and, more particularly, to an apparatus for locking an edge-of-dock type leveler in an upright rearward position to prevent accidental runoff of vehicles in use on the loading dock platform.
2. Description of Related Art
Forklift trucks and the like are frequently utilized on loading dock platforms to facilitate the loading and unloading of cargo carriers. Typically, however, forklift trucks cannot directly access the storage compartment of a carrier due to gaps and height variations between the platform and the carrier bed. To facilitate such access, a variety of methods have been developed; the most widely accepted of which is the dock leveler. Dock levelers are ramp-type apparatus generally designed to bridge the gap between the loading dock platform and a carrier bed, and to compensate for any existing height variations.
Typically, a dock leveler will have a center plate which pivots relative the loading dock platform and a lip plate which pivots relative a forward edge of the center plate. When the dock leveler is in use and fully extended, the lip plate rests directly on the bed of the carrier. As such, forklift trucks and the like can move freely between the loading dock platform and the carrier bed. When not in use, however, the dock leveler is typically stored with the center plate generally lying flush with the loading dock platform, and the lip plate hanging downwardly from the forward edge of the center plate. In this manner, the edge of the loading dock platform remains unobstructed, thereby creating the potential for a serious safety hazard.
Forklift trucks and the like can accidentally be driven off the unobstructed edge of a loading dock platform when the conventional dock leveler is in its standard storage position. This risk of accidental runoff is even greater due to the awkwardness in controlling forklift trucks, particularly those overladen with cargo. Likewise, loading dock platforms are frequently crowded with cargo and other obstacles, which further contributes to the difficulty in maneuvering around a loading dock and increases the potential for accidental runoff. Since loading dock platforms are typically elevated at least three feet from the ground, the consequence of accidental runoff can be disastrous both to equipment and personnel.
Recently, a few dock leveler designs have been developed to include various forms of automatic barriers to address the problem of accidental runoff. U.S. Pat. Nos. 4,920,598 and 5,040,298 disclose two different pit-mounted type dock levelers having automatic vehicle barriers. Although the dock levelers of U.S. Pat. Nos. 4,920,598 and 5,040,298 provide barriers against accidental runoff, several drawbacks in these designs are still quite evident. Most notably, pit-mounted type dock levelers tend to be expensive, both in construction and installation. This is particularly true when a pit-mounted type dock leveler is to be retrofitted into an existing loading dock platform.
Another common drawback of the dock levelers of U.S. Pat. Nos. 4,920,598 and 5,040,298 is the complexity of their designs. For example, the dock leveler of U.S. Pat. No. 4,920,598 requires that a hydraulically actuated assembly be mounted to the front of the dock leveler to permit both sliding and pivotal movement of the lip plate. This design complexity adds not only to the cost of construction, but also to the difficulty in both operation and maintenance. Due to the constant demands of loading and unloading carriers, loading dock personnel typically do not have the time to properly operate or maintain these complex dock levelers. However, attempts to short cut proper operating procedures often lead to injury of either the personnel or the equipment. This, of course, results in the added cost of medical care and replacement parts, as well as the loss in revenue during the "down time" of the loading dock.
An edge-of-dock type dock leveler has been marketed in the past to prevent a forklift truck from running off the loading dock platform at times when the dock leveler is in the stored position. This edge-of-dock leveler includes a lip plate pivotal about the outer edge of a center plate. To form a runoff barrier, the pivot axis for the lip plate is spaced from the rear edge of the lip plate. In this manner, when the dock leveler is moved into its standard stored position, i.e., with the center plate lying flush with the platform and the lip plate extending downward, the rear edge of the lip plate projects vertically above the center plate to prevent the accidental runoff of vehicles from the loading dock platform.
While the runoff barrier feature of this dock leveler has generally proven to be both effective and inexpensive, there remain two situations wherein the runoff barrier may prove to be a burden. The first occurs when actual use of the dock leveler is not required, such that the dock leveler is maintained in its standard stored position and a carrier is backed into a position adjacent the platform. In this instance, the upwardly projecting barrier may impede traffic between the platform and the carrier bed. The second circumstance occurs when the dock leveler is utilized, but the carrier is at such an elevation that the lip plate is not fully extended. Depending upon the angular difference between the center plate and the lip plate, vehicular movement into and out of the storage compartment of the carrier may again be obstructed.
Finally, a growing concern is the susceptibility of loading dock personnel to back strain and other injuries resulting from the operation of dock levelers. If not properly designed, the awkward positioning of an operating lever and the conventional pull-push motion required to extend a manual dock leveler could have harmful effects on an operator. Since the incorporation of hydraulic extenders would add tremendously to the cost of dock levelers, it is desirable to develop an inexpensive manually operated dock leveler which induces minimal back strain on the operator.